src/java/org/apache/cassandra/cql3/functions/masking/PartialMaskingFunction.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.cassandra.cql3.functions.masking;

import java.nio.ByteBuffer;
import java.util.Collection;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import javax.annotation.Nullable;

import com.google.common.annotations.VisibleForTesting;
import org.apache.commons.lang3.StringUtils;

import org.apache.cassandra.cql3.CQL3Type;
import org.apache.cassandra.cql3.functions.FunctionFactory;
import org.apache.cassandra.cql3.functions.FunctionName;
import org.apache.cassandra.cql3.functions.FunctionParameter;
import org.apache.cassandra.cql3.functions.NativeFunction;
import org.apache.cassandra.db.marshal.AbstractType;
import org.apache.cassandra.db.marshal.Int32Type;
import org.apache.cassandra.db.marshal.UTF8Type;
import org.apache.cassandra.exceptions.InvalidRequestException;

/**
 * A {@link MaskingFunction} applied to a {@link org.apache.cassandra.db.marshal.StringType} value that,
 * depending on {@link Type}:
 * <ul>
 * <li>Replaces each character between the supplied positions by the supplied padding character. In other words,
 * it will mask all the characters except the first m and last n.</li>
 * <li>Replaces each character before and after the supplied positions by the supplied padding character. In other
 * words, it will only mask all the first m and last n characters.</li>
 * </ul>
 * The returned value will allways be of the same type as the first string-based argument.
 */
public class PartialMaskingFunction extends MaskingFunction
{
    /** The character to be used as padding if no other character is supplied when calling the function. */
    public static final char DEFAULT_PADDING_CHAR = '*';

    /** The type of partial masking to perform, inner or outer. */
    private final Type type;

    /** The original type of the masked value. */
    private final AbstractType<String> inputType;

    /** Whether a padding argument hab been supplied. */
    @Nullable
    private final boolean hasPaddingArgument;

    private PartialMaskingFunction(FunctionName name,
                                   Type type,
                                   AbstractType<String> inputType,
                                   boolean hasPaddingArgument)
    {
        super(name, inputType, inputType, argumentsType(hasPaddingArgument));

        this.type = type;
        this.inputType = inputType;
        this.hasPaddingArgument = hasPaddingArgument;
    }

    private static AbstractType<?>[] argumentsType(boolean hasPaddingArgument)
    {
        // The padding argument is optional, so we provide different signatures depending on whether it's present or not.
        // Also, the padding argument should be a single character, but we don't have a data type for that, so we use
        // a string-based argument. We will later validate on execution that the string argument is single-character.
        return hasPaddingArgument
               ? new AbstractType<?>[]{ Int32Type.instance, Int32Type.instance, UTF8Type.instance }
               : new AbstractType<?>[]{ Int32Type.instance, Int32Type.instance };
    }

    @Override
    public Masker masker(ByteBuffer... parameters)
    {
        return new Masker(parameters);
    }

    private class Masker implements MaskingFunction.Masker
    {
        private final int begin, end;
        private final char padding;

        private Masker(ByteBuffer... parameters)
        {
            // Parse the beginning and end positions. No validation is needed since the masker accepts negatives,
            // but we should consider that the arguments migh be null.
            begin = parameters[0] == null ? 0 : Int32Type.instance.compose(parameters[0]);
            end = parameters[1] == null ? 0 : Int32Type.instance.compose(parameters[1]);

            // Parse the padding character. The type of the argument is a string of any length because we don't have a
            // character type in CQL, so we should verify that the passed string argument is single-character.
            if (hasPaddingArgument && parameters[2] != null)
            {
                String parameter = UTF8Type.instance.compose(parameters[2]);
                if (parameter.length() != 1)
                {
                    throw new InvalidRequestException(String.format("The padding argument for function %s should " +
                                                                    "be single-character, but '%s' has %d characters.",
                                                                    name(), parameter, parameter.length()));
                }
                padding = parameter.charAt(0);
            }
            else
            {
                padding = DEFAULT_PADDING_CHAR;
            }
        }

        @Override
        public ByteBuffer mask(ByteBuffer value)
        {
            // Null column values aren't masked
            if (value == null)
                return null;

            String stringValue = inputType.compose(value);
            String maskedValue = type.mask(stringValue, begin, end, padding);
            return inputType.decompose(maskedValue);
        }
    }

    public enum Type
    {
        /** Masks everything except the first {@code begin} and last {@code end} characters. */
        INNER
        {
            @Override
            protected boolean shouldMask(int pos, int begin, int end)
            {
                return pos >= begin && pos <= end;
            }
        },
        /** Masks only the first {@code begin} and last {@code end} characters. */
        OUTER
        {
            @Override
            protected boolean shouldMask(int pos, int begin, int end)
            {
                return pos < begin || pos > end;
            }
        };

        protected abstract boolean shouldMask(int pos, int begin, int end);

        @VisibleForTesting
        public String mask(String value, int begin, int end, char padding)
        {
            if (StringUtils.isEmpty(value))
                return value;

            int size = value.length();
            int endIndex = size - 1 - end;
            char[] chars = new char[size];

            for (int i = 0; i < size; i++)
            {
                chars[i] = shouldMask(i, begin, endIndex) ? padding : value.charAt(i);
            }

            return new String(chars);
        }
    }

    /** @return a collection of function factories to build new {@code PartialMaskingFunction} functions. */
    public static Collection<FunctionFactory> factories()
    {
        return Stream.of(Type.values())
                     .map(PartialMaskingFunction::factory)
                     .collect(Collectors.toSet());
    }

    private static FunctionFactory factory(Type type)
    {
        return new MaskingFunction.Factory(type.name(),
                                           FunctionParameter.string(),
                                           FunctionParameter.fixed(CQL3Type.Native.INT),
                                           FunctionParameter.fixed(CQL3Type.Native.INT),
                                           FunctionParameter.optional(FunctionParameter.fixed(CQL3Type.Native.TEXT)))
        {
            @Override
            @SuppressWarnings("unchecked")
            protected NativeFunction doGetOrCreateFunction(List<AbstractType<?>> argTypes, AbstractType<?> receiverType)
            {
                AbstractType<String> inputType = (AbstractType<String>) argTypes.get(0);
                return new PartialMaskingFunction(name, type, inputType, argTypes.size() == 4);
            }
        };
    }
}